feat: create migrator

internal/hub/migrations/20260415151037_create_agent_table.up.sql

@@ -0,0 +1,14 @@
+CREATE TABLE agents (
+    id BIGINT UNIQUE PRIMARY KEY,
+    agent_id VARCHAR(32) UNIQUE NOT NULL,
+    agent_name VARCHAR(255),
+    architecture VARCHAR(10) NOT NULL,
+    system VARCHAR(10) NOT NULL,
+    hostname VARCHAR(100) NOT NULL,
+    version VARCHAR(10) NOT NULL,
+    capabilities JSON,
+    registered_at timestamp without time zone DEFAULT now() NOT NULL
+);
+
+CREATE UNIQUE INDEX idx_agent_id ON agent (id);
+CREATE UNIQUE INDEX idx_agent_id_id On agent (agent_id)